Interpretive Summary: Melon (Cucumis melo L; 2n = 2x = 24) is an economically important, cross-pollinated vegetable species. Although melons are grown worldwide, Asia produces more than 71% of the total world tonage. The United States of America is the third most prolific melon producer (behind China and Turkey), where ~37,000 ha provides a $400 million (USD) return to its economy. The inheritance of yield in melon is complex, and is associated with component traits including days to anthesis, primary branch number, fruit number, fruit weight per plant and average weight per fruit. These components are associated with fruit maturity. The nutritional value of melon is variable, and dependent upon the market class, genotype, and growing environment (Lester and Eischen 1995). Fruits of internal orange-fleshed market types (e.g., U.S. Western Shipping types), for instance, are a rich source of dietary carotenes (primarily ß-carotene, which is a precursor of Vitamin A). Information on the genetic control (i.e., inheritance) of fruit maturity and its relationship with ß-carotene fruit content is not known. Therefore, a study was designed to elucidate the genetics of fruit maturity (i.e., number of days from sowing to first mature fruit) and the quantity of ß-carotene in melon. It was determined that many genes control both fruit maturity and ß-carotene content in fruit. These data can be used by plant breeders to devise effective strategies to improve the earliness (entry into the market place) and ß-carotene (improved human health) of melon. The release of improved melon for these characteristics will make the U.S. grower more competitive in a growing global market place.

Technical Abstract:
Melon (Cucumis melo L.) fruit production in U.S. can be improved through the introgression of early fruit maturity (FM) and the enhancement of fruit color [i.e., quantity of ß-carotene (QßC); orange fruit mesocarp]. However, the genetics of FM and QßC have not been clearly defined in U.S. Western Shipping market class melons (USWS). Thus, a cross was made between the monoecious, early fruit maturity Chinese line ‘Q 3-2-2’ (non-carotene accumulating, white-fleshed mesocarp) and the andromonecious, comparatively late fruit maturity USWS line ‘Top Mark’ (orange-fleshed mesocarp) to determine the inheritance of FM and QßC in melon. Parents and derived cross-progenies (F1, F2, F3, BC1P1, and BC1P2) were evaluated for FM and QßC at Hancock, Wisconsin over two years. Significant (p = 0.001) genotype x environment (years) interactions were detected for FM, but not for QßC in F3 families. Estimates of narrow-sense heritability (h2N) for QßC and FM as defined by F1, F2, and BC (by individuals) were 0.55 and 0.62, respectively, while estimates based on F3 families were 0.68 and 0.57, respectively for these traits. Although color segregation (in F2 and BC1P2 progenies) suggests the action of two recessive epistatic loci, the model could not be confirmed by F3 family segregation. Significant phenotypic or genetic correlations between these traits were not detected. Although the inheritance of QßC and FM is complex, introgression (e.g., by backcrossing) of early FM genes resident in Chinese germplasm into USWS market types is possible. Such introgression may lead to increased yield potential in USWS market types while retaining relatively high ß-carotene fruit content (i.e., orange flesh), if stringent, multiple location and early generation family selection (F3-4) is practiced for FM with concomitant selection for QßC.